Cycles, animate the color on part of an object
Create a new material for the part that you want to change and assign it to the section of the mesh you want to affect. 

(see : Add different materials to different parts of a mesh?)


Then the color change can be done in different ways.

Then over over the color of the material, add a keyframe. Change to a different frame, change the color and add another keyframe.



A different way would be to use an RGB mix node to contol the color of your object and animate the factor value:



Or Create two different shaders with the qualities you are after, add a mix shader node and animate the way they mix.